Editor's Notes:

Displays the contents of a displayed draggable rectangle on one axis of a source figure into an axis in a target figure. The difference in the screen size of the target axis and the size of the rectangle represents the magnification factor that the contents of the source rectangle will appear in the target figure.

Backwards compatible to R12.1 at least. Much smoother under R14x though.

Update of 3/29:
1) Put in arrow keys to have individual control over rectangle width and height
2) Saved size state of rectanglebetween drags and added 'r' key to restore default rectangle proportion (20% of axes)
3) Added 'm' key to toggle between maximizing target axis and having it be the original. Also, 'm' as argument to default to maximized vs orignal size.
4) Tried to fix wierd event timing bugs that would result in residual rectangles. The biggest fix came by disallowing the right mouse button.